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Old 04-17-2014 | 04:32 AM
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sensei
 
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From: SAN ANTONIO, TX
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Originally Posted by Hydro Junkie
I'm going to disagree with you on some points of your post:
1) for a full cure and for the epoxy to reach full strength it must be cured above 70 degrees
2) If you are building in a cold environment your glue joints will not be as strong as they would be had the epoxy been cured at a higher temp
Per the West Systems website:
Each hardener has an ideal temperature cure range. At any given temperature, each resin/hardener combination will go through the same cure stages, but at different rates. Select the hardener that gives you adequate working time for the job you are doing at the temperature and conditions you are working under. The product guide and container labels describe hardener pot lives and cure times.
At no time does the manufacturer make any reference to strength and heat being inter-related. In fact, the website actually states:
CAUTION! Heating epoxy that has not gelled will lower its viscosity, allowing the epoxy to run or sag more easily on vertical surfaces. In addition, heating epoxy applied to a porous substrate (softwood or low-density core material) may cause the substrate to "out-gas" and form bubbles in the epoxy coating. To avoid out-gassing, wait until the epoxy coating has gelled before warming it. Never heat mixed epoxy in a liquid state over 120°F (49°C).
In a commercial manufacturing application, the chemical makeup of the epoxies used are different than what we as consumers and modelers will have access to through common sources. Years ago, I was working at Hexcel where we used pre-preg materials with varying epoxy compounds in the fabrication of aircraft parts. To increase strength and decrease cure time, the parts were vacuum bagged to 29" of vacuum and baked in an oven slightly hotter than you indicated. The vacuum bagging was what increased the strength, compressing the fabrics more tightly together and removing almost all of the air in and between the plys. The heat only decreased cure time and melted the epoxy coating so that it could flow between the fibers and actually "grab" the fabric plies, holding them together and filling the weave to make a solid, windproof surface.
If you really understood what speed was saying, you would realize that he simply meant they post cure all epoxies @ 160 degrees without spelling it out for you, plain and simple.

The caution label from West Systems is really for the unknowing hobby types because there are many manufacturing applications that require heating epoxy resins well over 120 degrees as part of the processing.

You have stated heat is only used as a processing means to decrease the cure time when utilizing pre-pregs as your manufacturing media. You might consider staying away from entering into disagreements on a subject you have clearly illustrated you possess limited knowledge of.

Bob